The word "catholic" has fallen into sad disrepute amongst evangelicals, who are generally only aware of its use by the Roman Catholic Church. It is generally thought to be the opposite of Protestant, and the older and more accurate meaning - "universal" had been all but lost. This is unfortunate. As a Protestant, and indeed and evangelical, I am concerned that I also be a catholic: and I am concerned that you join me in this concern. Let me tell you why.
1. To be catholic is to be concerned for the whole church
It is all too easy for us to be bothered only about things that happen in our denomination, or amongst the sorts of Christians we like to identify with. Generally speaking, even the most broad-minded evangelicals only extend their interests to other evangelicals. But to be catholic is to be concerned for all those who name the name of Christ - even where one considers them to be in grave theological error. I think we need to spend more time praying for those believers who fall outside our immediate circles.
2. To be catholic is to acknowledge a debt to history
We evangelicals have a bothersome tendency to think that we invented the gospel - or at least that nobody throughout church history understood it quite so well as we do. So we tend to just read books by our contemporaries who say the same things we would say in exactly the same way we would say them. (The more thoughtful evangelicals would date the invention of the gospel to the 16th century, of course, but this is only a little better). To be catholic is to acknowledge the long line of believers through the millennia who have faithfully witnessed to Christ - and not just to acknowledge them, but to read them! The bookshelf is probably the most practical way that the communion of saints manifests itself.
3. To be catholic is to learn from the whole church
Because everything that is really Christian belongs to the church, we can be free to take truth from whatever source it comes - always being discerning and testing by Scripture, of course. So if the Pope has something good to say - and he often does - I can claim that. All truth is Christ's truth, and Christ is given as head to the church which is his body. I often find that the things that challenge me, make me think and grow my understanding of the gospel come from outside my own tradition.
4. To be catholic is to speak to the whole church
Obviously I can't actually address the whole of Christendom. But all too often as evangelicals, our thinking and speaking becomes an intra-evangelical discussion with no intention to engage with and confront others. Worse, it can become an intra-Anglican discussion, or an intra-baptist discussion. And so we become concerned only to confess the faith of our party, only to reform our party, only to grow our party. But to be catholic means to confess one's faith to the whole church, calling the whole church to examine it and, if it is the faith of Scripture, to get in line with it. As a "credo baptist" (horrible phrase, but don't have a better) I declare to the whole church that I am convinced Scripture teaches this: and if I am so convinced, I cannot be satisfied to allow any part of the church to ignore it.
I think the world could do with seeing some more catholic protestant orthodox evangelicals...